Glycogen Metabolism

Question 1

What is glycogenesis?

Answer 1

synthesis of glycogen from glucose

Question 2

What is glycogenolysis?

Answer 2

breakdown of glycogen to form glucose

Question 3

What is gluconeogenesis?

Answer 3

de novo synthesis of glucose from metabolic precursors (lactate, amino acids, glycerol)

Question 4

What is glycogen?

Answer 4

Main storage form of glucose in liver and muscle cells

Question 5

What is the use of liver glycogen?

Answer 5

broken down between meals and released to maintain blood glucose levels for red blood cells and brain

Question 6

What is the use of muscle glycogen?

Answer 6

it is not able to be used for the maintenance of blood glucose levels
it provides energy via glycolysis and the TCA (kreb’s cycle) during bursts of physical activity

Question 7

When is gluconeogenesis the main source of blood glucose?

Answer 7

overnight when the hepatic glycogen is depleted

Question 8

What is the structure of glycogen?

Answer 8

it is a polymer of glucose molecules
the molecules are joined by alpha 1-4 glycosidic links
the branches are joined to the chain by alpha 1-6 glycosidic links

Question 9

How are glucose molecules added to the glycogen chain?

Answer 9

glucose residues can only be added to an existing chain
there needs to be a glycogen primer with at least 4 glucose residues
the primer is covalently attached to a protein called glycogenin

Question 10

What enzyme converts glucose to glucose-6-phosphate?

Answer 10

hexokinase

Question 11

What enzyme converts glucose-6-phosphate to glucose-1-phosphate?

Answer 11

phosphoglucomutase

Question 12

What enzyme converts glucose-1-phosphate to UDP-glucose?

Answer 12

UDP-glucose pyrophosphorylase

Question 13

What enzyme converts UDP-glucose to [glucose]n+1 + UDP?

Answer 13

glycogen synthase

Question 14

What molecule within the glycogen synthesis process can enter into glycolysis?

Answer 14

glucose-6-phosphate

Question 15

What is considered to be an active form of glucose?

Answer 15

UDP-glucose

Question 16

What is released upon the hydrolysis of the phosphate ester linkage in a nucleotide sugar?

Answer 16

energy

Question 17

How is glycogen synthesised from UDP-glucose?

Answer 17

One glucose molecule is added to glycogen at a time
Can only extend the chains of glycogen, it can not start new molecules
Can not introduce branches
Rate limiting enzyme of glycogenesis

Question 18

What enzyme introduces branching to the glycogen?

Answer 18

transglycosylase, introduces alpha 1-6 glycosidic branches into glycogen
approximately every 10 glucose residues

Question 19

What enzyme catalyses the formation of glucose-1-phosphate in glycogenolysis?

Answer 19

glycogen phosphorylase

Question 20

what are [glucose]n + phosphate (Pi)

converted to in glycogenolysis?

Answer 20

glucose-1-phosphate + [glucose]n-1

Question 21

How many glucose molecules can be cleaved from a glycogen molecule at once?

Answer 21

1 glucose molecule is cleaved off the ends of glycogen at a time

Question 22

What is the second step in glycogenolysis?

Answer 22

glucose-1-phosphate is converted to glucose-6-phosphate

Question 23

What happens to the glucose-6-phosphate molecule produced by glycogenolysis in the liver?

Answer 23

glucose 6-phosphate can be de-phosphorylated and the resulting glucose released into the blood stream

Question 24

What happens to the glucose-6-phosphate molecule produced by glycogenolysis in the skeletal muscle?

Answer 24

it is used to provide energy via glycolsis and the TCA (krebs) cycle as t can’t be phosphorylated

Question 25

what conditions require the process of gluconeogenesis?

Answer 25

prolonged starvation

Question 26

What are the precursors which are used to synthesise new glucose through glucneogenesis?

Answer 26

Lactate - skeletal muscle synthesizes in anaerobic conditions Amino acids - derived from muscle protein through proteolysis Glycerol - derived from triglycerides by lipolysis in adipose tissue

Question 27

How is the energy for the gluconeogenesis ontained?

Answer 27

through the oxidation of fatty acids released from adipose tissue

Question 28

Where does gluconeognesis take place?

Answer 28

mainly in the liver but a small bit in the kidneys

Question 29

Is gluconeogenesis essentially the reverse of glycolysis?

Answer 29

NO gluconeogenesis is NOT the reverse of glycolysis

Question 30

What 3 essentially irreversible enzyme reactions are there in glycolysis?

Answer 30

hexokinase phosphofructokinase pyruvate kinase

Question 31

How does glucogenesis bypass the irreversible reactions of glcolysis?

Answer 31

- uses 4 unique liver enzymes - synthesises oxaloacetate in mitochondria the TCA cycle intermediate (oxaloacetate is important for accepting acetyl groups from fat breakdown) - is an energy consuming process

Question 32

Gluconeogenesis | 2 pyruvate + 4 ATP + 2 GTP + 2 NADH + 4 H+ + 6 H2O

Answer 32

glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+ + 2 H+

Question 33

What is the Cori cycle?

Answer 33

The cycle of lactate prodution in muscle cells through anaerobic respiration and the synthesis of glucose from lactate in the liver. This glucose is then carried in the bloodstream back to the skeletal muscle for further anaeorbic respiration

Question 34

How are amino acids used as a precursor for gluconeogenesis?

Answer 34

Different amino acids enter the TCA cycle at different positions but ultimately lead to the synthesis of oxaloacetate and glucose

Question 35

What are the 2 hormones which regulate glycogenolysis and gluconeogenesis?

Answer 35

Glucagon | Insulin

Question 36

What does high AMP or ADP indicate?

Answer 36

That the cell is low in energy

Question 37

What does high ATP indicate?

Answer 37

That the cell is high in energy

Question 38

What does fructose 2,6-bisphosphate levels show?

Answer 38

high levels - in fed state | low levels - in starved state

Question 39

What do high levels of citrate, alanine and acetyl-CoA indicate?

Answer 39

that the intermediates or building blocks abundant

Question 40

How does insulin affect the enzymes involved in glucogen synthesis and lysis?

Answer 40

it inhibits glycogen phosphorylase decreasing the conversion of glycogen to glucose-1-phosphate it promotes glycogen synthase increasing the conversion of UDP-glucose to glycogen

Question 41

How does glucagon affect the enzymes involved in glucogen synthesis and lysis?

Answer 41

it inhibits glycogen synthase decreasing the conversion of UDP-glucose to glycogen it promotes glycogen phosphorylase increasing the conversion of glycogen to glucose-1-phosphate

Question 42

What hormones increase the activity f glycogen phosphorylase?

Answer 42

glucagon adrenaline cortisol